The present invention relates to a method for determining the position of at least one fixed cartography token of an automaton. The invention applies in particular to automated in-vitro diagnosis devices, in particular in the field of haemostasis.
Such a device or automaton comprises a fixed frame on which plates are fixed, comprising housings for positioning containers in the form of bottles, tubes or reaction bowls. The device comprises, for example, a plate intended to support bottles containing reactive products, a plate intended to support tubes containing plasma samples, and a plate intended to support reaction bowls in which measurements are made.
The device further comprises one or more motorised arms each comprising a head able to move according to cartesian coordinates (X, Y, Z) or cylindrical coordinates (θ, r, Z) and equipped with a pipette/needle assembly or a gripping system for moving the bowl from one station to another.
Part of such an automaton is for example known from the document FR 2 764 703 in the name of the applicant.
The needle (or pipette) is conventionally equipped with capacitive detection means, making it possible in particular to detect the position as from which the needle comes into contact with the liquid. Such detection means are generally referred to by the English acronym LLD (standing for liquid level detection).
In general terms, it is necessary to precisely control the position of the end of each needle with respect to the various containers, so as to avoid the needle striking the edge or bottom of a container, which may cause breakage or deformation of the needle, or damage to the container causing contamination of the reactive product or of the sample to be analysed.
However, producing such a device necessarily gives rise to uncertainties in positioning, due for example to the method of manufacturing each part of the device (manufacturing tolerances, etc), to the method of assembling the various parts with respect to one another (assembly clearances, imprecision during assembly, etc), or to the method of moving the arm equipped with the movable head on which the needle is mounted (control by means of stepping motors for example).
There therefore exists a need to precisely determine the positions of the various containers fixed with respect to the movable needle.
For this purpose, the patent EP 1 354 185 proposes using cartography tokens, the positions of which with respect to the containers are known. Each token has a roughly cylindrical shape, the top end of which comprises a blind hole. Pipettes or needles are mounted on a movable head actuated by an arm that can be moved along X, Y and Z orthogonal to one another. The needles are in particular brought into contact with the internal surface of the blind hole, so as to precisely determine the positions of the cartography tokens fixed with respect to the movable needles.
During such a method, the reactive products or the samples contained in some needles may soil the blind holes and may cause contamination of the other needles. In order to avoid this, it is necessary to clean the cartography tokens, which is relatively tedious when they comprise blind holes with a diameter slightly greater than the needle.